Drink produced from honey and nuts, packed with energy (4)
I believe the answer is:
mead
'drink' is the definition.
(mead is a kind of drink)
'nuts packed with energy' is the wordplay.
'nuts' becomes 'mad' (informal term).
'packed with' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'mad' enclosing 'e' is 'MEAD'.
'produced from honey and' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mead that I've seen before include "The poetic field" , "Cornish drink" , "Drink made of fermented honey and water" , "Honeyed drink for dame" , "US anthropologist, Margaret d. 1978" .)